Chapter 4 - Physical Development and Health Flashcards
2 PATTERNS of PHYSICAL GROWTH
PHYSICAL GROWTH generally follows two PATTERNS:
1) The CEPHALOCAUDAL PATTERN, or the sequence in which the fastest growth always occurs at the top—the head. Physical growth in size, weight, and feature differentiation gradually works its way down from the top to the bottom.
2) The PROXIMODISTAL PATTERN, the growth sequence that starts at the center of the body and moves toward the extremities.
GROWTH in INFANCY and CHILDHOOD
The average newborn is 50 cm long and weighs 3.5 kg. Growth proceeds rapidly during the first year of life, with infants doubling their weight in 4 months, tripling it by their first birthday and gaining 2.5 cm per month. Growth slows considerably during the second year - the average 2 year-old is 85 cm tall.
During CHILDHOOD body fat declines slowly but steadily. Growth patterns show much inter-individual variability, due mostly to heredity and in part to environmental experiences - height and weight largely reflect nutrition. Some children are unusually short - this could be the consequence of congenital factors, growth hormone deficiencies, or physical problems such as malnutrition. Congenital problems can be treated with hormone therapy, which targets the pituitary gland, responsible of the natural release of growth hormone. If problems are properly treated, usually typical growth is attained.
GROWTH in ADOLESCENCE - PUBERTY
PUBERTY is a period of rapid physical maturation involving hormonal and bodily changes that occur primarily in early adolescence.
There are wide variations in the onset and duration of puberty - 10 to 14 years of age for girls and 12 to 16 for boys. There has been a steady decrease of the age of puberty onset in the last decades, probably due to improved nutrition and health conditions: the average age of MENARCHE - a girl’s first menstruation -dropped an average of two to four months per decade for much of the twentieth century.
PRECOCIOUS PUBERTY is diagnosed if pubertal onset occurs before 8 years of age in girls and before 9 years of age in boys. It generally leads to short stature, early sexual maturation and age-inappropriate behavior - it typically is treated by endocrinology interventions, which temporarily stops pubertal change.
Puberty produces a GROWTH SPURT and SEXUAL MATURATION. Male pubertal changes include increase in penile and testicle size, pubic, facial and body hair growth and voice changes. Female pubertal changes include breast enlargement, widening of the hips, pubic hair growth and the beginning of the menstrual cycle with the MENARCHE.
Puberty is programmed into the genes, but environmental factors, such as family influences and stress, can also influence its onset and duration. Nevertheless, it is initiated and guided by HORMONES, chemical substances secreted by the endocrine glands and carried through the body by the bloodstream. Secretion of key hormones for puberty is regulated by the interaction of the HYPOTHALAMUS, PITUITARY GLAND and the GONADS - testes in males, ovaries in females. ANDROGENS - TESTOSTERONE especially - are the main class of male sex hormones. ESTROGENS - particularly ESTRADIOL - are the main class of female sex hormones.
PSYCHOLOGICAL DIMENSIONS of PUBERTY.
Two of the most pronounced psychological changes during puberty involve:
1) BODY IMAGE: adolescents are preoccupied with their bodies and develop images of what their bodies are like. Generally speaking, girls are less happy with their bodies and have more negative body images than boys throughout puberty. Nonetheless, research suggests that both boys’ and girls’ body images became more positive as they moved from the beginning to the end of adolescence.
2) EARLY and LATE MATURATION: when adolescents mature earlier or later than their peers, they often perceive themselves differently and their maturational timing is linked to their socio-emotional development. Early-maturing girls are more likely to smoke, drink, be depressed, have an eating disorder, engage in delinquency, struggle for earlier independence from their parents, and have older friends.
The NEUROCONSTRUCTIVIST VIEW
The NEUROCONSTRUCTIVIST VIEW holds that:
(1) biological processes and environmental conditions influence the brain’s development;
(2) the brain has plasticity and is context dependent;
(3) development of the brain is closely linked with the child’s cognitive development.
It emphasises the importance of considering interactions between experience and gene expression in the brain’s development.
SLEEP in INFANCY
Newborns sleep 16 to 17 hours a day - initially, their sleep during the day does not always follow a rhythmic pattern. By about 1 month of age, most infants have begun to sleep longer at night and by 6 months of age, they usually have moved closer to adult-like sleep patterns - spending their longest span of sleep at night and their longest span of waking during the day. The most common infant sleep-related problem is night- time waking.
A much greater amount of time is taken up by REM sleep in infancy than at any other point in the life span - about half of an infant’s sleep is REM sleep, and infants often begin their sleep cycle with REM sleep rather than non-REM sleep. The large amount of REM sleep may provide infants with added self-stimulation, since they spend less time awake than do older children. REM sleep also might promote the brain’s development in infancy
SHARED SLEEPING is a controversial issue, for some child experts praise its benefits - it promotes breast feeding, lets the mother respond more quickly to the baby’s cries, and allows her to detect breathing pauses in the baby that might be dangerous - while others warn against its drawbacks - it might result in disrupted sleep for parents, it is linked with a greater incidence of SIDS.
SUDDEN INFANT DEATH SYNDROME (SIDS) occurs when infants stop breathing, usually during the night, and die suddenly without an apparent cause. Risk of SIDS is highest at 2 to 4 months of age and putting infants to sleep on their back has been proved to be the most effective method to reduce such risk. Several factors influence risk of SIDS, such as abnormalities in brain stem functioning, low birth weight, socioeconomic status and pre and postnatal exposure to smoke.
SLEEP in ADOLESCENCE
There has recently been a surge of interest in adolescent sleep patterns focused on the belief that many adolescents are not getting enough sleep. Teenagers need 9.5 h of sleep each night to be optimally alert, and the average teenager sleeps 7.5 hours per night - this creates sleep debt, which is linked with risk-taking behaviours, and less effective attention.
Older adolescents are often more sleepy during the day than are younger adolescents - adolescents’ biological clocks undergo a hormonal phase shift as they get older. This shift is caused by a delay in the nightly presence of the hormone melatonin, which is produced by the brain’s pineal gland and prepares the body for sleep.
